Hi everybody,

I just bought a 1991 300D 2.5. The car idles steady at 600-700 rpms, but misses. Also it lacks low end response - its very slow in 1st gear. The previous owner cleaned the injectors "after a bad tank of diesel" , but did not replace the heat shields. So on three injectors there were bubbles and fuel comingro the injector threads to the head. The car runs fine on the highway though.

I replaced the heatshields and cleaned the carbon on the injectors and the head. So now they seal fine. But the car runs on 4 cylinders. If I loosen the metal lines to each injector one by one, each one makes a difference in idle except number 4. I took off the metal line to #4 completely while idling, and it just drips like two drops per second. You can see the pulses from the pump, but barely any fuel coming out. The injector has carbon buildup, so the cylinder is running. Like i mentioned, on the highway the car feels normal. Also the clear fuel filter looks frothy, has air in it.

I ran two cans of diesel purge and changed the clear filter, same problem. I changed the injector with another one, same thing.

Should I replace the delivery valve o-rings/washers? I read on a forum that somebody had a similar problem with the car, and the delivery valves were not leaking, but the o-rings were bad...

Or my pump is out?

Thanks!